Snap-acting springing and thermostatic plate



Nov. 8, 1949 M. WILSON 2,487,683

SNAP-ACTING SPRINGING AND THERMOSTATIC PLATE Filed May 10, 19 46 2 Sheets-Sheet 1 Nov. 8, 1949 H. M. WILSON 2,487,683

SNAP-ACTING SPRINGING AND THERMOSTATIC PLATE Filed May 10, 1946 2 Sheets-Sheet 2 FIGS. FIG.9.

Patented Nov. 8, 1949 SNAP-ACTING SPRINGING AND 'rnaamos'rs'rrc PLATE Harold M. Wilson,

Lexington, Mass., assignor to Metals & Controls Corporation, Attleboro, Masa, a corporation of Massachusetts Application May 10, 1946, Serial No. 668,865 11 Claims. (01. 200-138) This invention relates to snap-acting plates, and with regard to certain more specific features, to snap-acting control devices including inherently snap-acting temperature-responsive means,'particularly adapted to operate valves, switches, and the like. The invention also relates to a method of making such plates.

Among the several objects of the invention may be noted the provision of inherently snapacting devices, particularly thermostats, which respond to suitable actuation with an improved snap or abrupt motion, and which have a greatly increased range of usable motion; the provision of a thermostatic electric switch which is com-- pact in structure and which, comprising only one movable part, is relatively simple and economical to construct; the provision of a thermostatic switch which is relatively simple to adjust; the provision of a thermostatic switch of the snap-acting disc type. so constructed that a much greater portion of the snap motion can be eiiectively utilized; the provision of a thermostatic switch which is less subject to creeping during the closed part of its cycle than hitherto known switches of like class; and the provision of a thermostatic switch which has a greater certainty of operation. Other objects will be in part obvious and in part pointed out hereinafter.

The invention accordingly consists of the elements and combinations of elements, steps and sequence of steps, features of construction and manipulation, and arrangements of parts, which will be exemplified in the accompanying drawings, and the scope of the application of which will be indicated in the following claims.

I In the accompanying drawings, in which are illustrated two of various possible embodiments of the invention,

Fig. l is a top plan view of an inherently snapacting device of the present invention;

Fig. 2 is a side elevation of the snap-acting device of Fig. 1;

Fig. 3 is a cross section along line 33 of Fig. 1;

Fig. 4 is a left-end elevation of Fig. 1;

Fig. 5 is a side elevation on a reduced scale of a thermostatic switch employing the snapacting device of Fig. 1;

Fig. 6 is a left-end elevation of Fig. 5;

Fig. 7 is a view similar to Fig. 5 but showing an alternative position of the snap-acting element;

Fig. 8 is a view similar to Fig. 2 but showing another embodiment of the invention;

taken substantially Fig. 10 is a left-end view on a reduced scale of Fig. 8;

Fig. 11 is a view similar to Fig. 6 but showing the alternative form of the invention in application; and,

Fig. 12 is a vertical section taken on line |2--l 2 of Fig. 11, but showing also the alternative use of an anchor part.

Similar reference characters indicate corresponding parts throughout the several views of the drawings.

The invention is an improvement upon the structures shown in United States Patents 1,448,- 240 and 2,317,831. Cross reference is hereby made under the provisions of Rule 78 to the assignees copending application Serial No. 697,879, filed September 19, 1946, for Snap-acting springing and thermostatic plates.

The present invention applies to control devices of all types wherein it is desired that the controlling element shall move with a snap motion. Among such control devices are valves and electric switches, which constitute the more usual controlled or actuated elements falling within the scope of the invention. The invention, in principle, applies equally well to these and other types of control devices, but for purposes of description, the application of the invention to thermostatic switches will sufflce.

Inherently snap-acting thermostatic plates or elements generally have the disadvantage that the available snap movement is small. In order to increase this movement, multiplying switch arms have been used, but these lead to additional cost and complexity in the device. Another solution to the diiiiculty has been to mount a snapacting plate at one end thereof, and utilize the motion of an opposite end or part of the plate. This has been done both with and without restraining the motion of the central part of the snap-acting plate. Where no central restraint is used. a disadvantage is encountered, in that to adjust the thermostatic plate so as to eliminate the inherent initial creep or slow motion part of the movement. of the plate, it is necessary to pre-rstress the plate, generally by bending the supporting mounting. However, inasmuch as these snap-acting plates are flexible, this bending tends to strain a part of the snap-acting plate toward the opening position, and when the plate has snapped to a position of opposite curvature, it is found that a large part of the snap motion has, for useful purposes, been lost Memes because of this strain. Where a central restraint is used, the disadvantage is that the addition of the center adiusting means leads to additional cost of ,manufacture, plus the further object on that, due to the clearance that must be allowed between the snap-acting plate and the shoulders of the adjusting stem to prevent binding, additional creep is allowed during the return motion of the plate, with resulting loss of usable snap motion.

By means of this invention a control device is provided (exemplifiedin a thermostatic switch), wherein the snap-acting plate is mounted at one end, and the other free end thereof is used for control purposes. The snap-acting plate is so formed that (l) substantial elimination of the initial creep of the plate, and (2) adjustment of the operating temperature of the snap-acting plate, are both accomplished without encountering the difficulty mentioned above in respect to pro-springing or pre-straining the snapeacting plate and thus losing useful motion, and without the additional cost of a central adjusting post.

particularly to the drawing, numeral l indicates in general a permanently set dished snap-acting thermostatic plate composed of thermostatic bimetal. It comprises a round disc-shaped portion 2 having at least one projecting mounting ear 3 and it may have another ear 4. A central hole 5 is provided, if desired.

Extending from approximately the outer end of the ear 3 to approximately the center of the plate (or beyond, if desired) is a raised (or alternatively depressed) rib 6. Rib 6 serves as a stiflening element for the mounting-end portion of the snap-acting plate and in addition, tends to mantain the center of the plate in a predetermined position. In order to elminate the initial slow motion of .the element and to adjust its operating temperature, only a l ght bending of the mounting support need be made, and little or no canting of the plate toward the closed position is c-fitcted, since sumcient stress can now be put in the plate with little canting.

Another improvement afforded by this invention is the reduction of creep in relation to a fixed point of reference exterior of the plate.

Figs. 1--'! show a case wherein the rib is raised. Figs. 8- .2 show a case wherein the rib is depressed. Either alternative will work satisfactorily. 7

It is to be noticed that in this snap-acting Referring now more.

plate, a permanently set portion of the plateextending from approximatelyone side I of the rib B circumferentially around the plate to the other side 8 of the rib 6 is of a non-developable contour. That portion of the snap-acting plate surface which comprises the rib itself is of developable contour. The invention, therefore, provides a snap-acting plate in which the surface of the plate is partly non-developable and partly developable. The re-entrant boundary of the non-developable surface is not necessarily a sharply defined boundary. It may change gradually from its non-developable character into the developable character of the rib B.

For the purposes of using this snap-acting plate a contact element 9 is welded to the ear 4.

Fig. 5 shows a thermostatic snap-acting switch employing the snap-acting element of Fig. 1. A base ill of insulating material such as Bakelite" or micarta is provided. Mounted adjacent to each end of the base it are studs ii and i2 which project on both sides of the base It. Studs II and II can be fastened into the base it by any of the means well known in the art. such as riveting or the like. These studs are made of steel, or some other metal capable of being spot welded in the usual type of spotwelding machine. The lower ends I! and I4 respectively of studs II and I2 are threaded to serve as connecting terminals. The upper portion i5 of the stud ii is reduced in cross section, as shown, by milling away a partof the stud to leave a reduced cross section at IS which is capable of being bent. This to to provide adjustment for the snap-acting plate I. A flat table portion I6 is preferably left on stud II to serve as a mounting table for the ear 1 of plate I.

Plate i is mounted on table I6 by spot welding the horizontal flanges l1 and is of the ear 3 to the top surface of table l8. Mounted on the top end of stud I2 is a contact ID. This mountin can be accomplished either by spot welding or by soldering or brazing. The relative heights of table It and the top part of stud I2 are preferably so proportioned so that when plate i is welded to table It, conta it 9 is just touching contact ii.

In the manufacture of the assembly, the milling operation to form the reduced section ii of stud ll may be done after stud II is firmly mounted in base iii. In this way, the milling can i be done in such a direction as to provide a reduced cross section in the direction in which i! is to be bent for temperature adjustment.

After plate i has been mounted on stud IS, the temperature adjustment is made by bending stud l5 clockwise or anti-clockwise, as may be found necessary in order to place the proper tension in plate I in order to eliminate the initial creep or slow motion of the plate and to adjust the operating temperature. The amount of bending is governed by the individual characteristics of each plate.

Fig. 7 shows the position occupied by the snapacting plate when it has operated to snap to a position of opposite curvature. Fig. 11 shows the construction when the plate of Figs. 8-10 is used. In this case, a groove 20 is provided in table l6 to accommodate the depressed rib 26. This groove may be milled in table l6 after the stud II is firmly riveted into the base II, and will then provide a locating and aligning means for plate i. Again, the ear 3 of the plate is welded to the table IS. A contact construction similar to that above described is provided for the other end of the snap-acting plate. Similar adjusting is made in order to eliminate initial creep, and to have the plate operate at its correct temperature.

Fig. 12 is a vertical section showing the parts of Fig. 11. except that a strengthening feature has been shown. This consists in a thin disc 3| of cold rolled steel which at the time that the ear 3 is welded to the table I6 is also welded to the ear above the depressed rib 26. Thus the ribbed portion of the ear 3 is enclosed on opposite sides by welded parts.

Exemplary dimensions are a thickness of .012 inch for the disc portion 2 for a diameter of this portion of approximately .875 inch. The central hole 5 is approximately .157 inch. The widths of the ears 3 and 4 are approximately .312 inch. The inside radius of the rib in both forms of the invention (whether struck up or struck down) is approximately .032 inch. The disc 3| is approximately inch thick and A inch in diameter.

These dimensions are of course subject to variation, depending upon the service to which the device is to be put.-

It is clear that the snap-acting plate may be a mono-metallic snap-acting spring plate, if it is desired to construct a simple manually operable snap switch, without response to temperature. All the attendant advantages of this invention over prior art snap switches also inhere in such a construction. It is also clear that a separate reini'orcing rib may be attached to the plate, as distinguished from a rib which is made an integral part of the plate as shown. This would-be accomplished by welding or the like.

The advantages of the invention may also be realized, at least in part, even in a snap-acting plate which does not have ears. In such a case, the rib will preferably extend simply from the peripheral portion of the plate to a central portion thereof. The stiffening of the one side of the plate will diminish the eflective creep of the disc.

The terms developable" and "non-developable" are used herein according to their usual geometric meanings. For example, a spherical form for shape 2 is non-developable, and a cyllndric or conical form for the form 8 is developable. There are also other known shapes in these categories but the above are sufllciently exemplary. The term "permanently set: is used herein according to the usual meaning in the field of strength of materials, meaning a permanent change in form occasioned by stressing of material beyond its elastic limit.

In making the device itis preferable that the developable surface be first formed, and' thereafter the non-developable surface, because once a non-developable characteristic is imparted to a given area, it is difllcult by a subsequent formation in the'same area to eliminate the non-developable characteristic. It is also easier to make the non-developable form around the small channel effected by the developable form.

Figs. 5, 6, 7 and 11 (which are on a reduced scale) indicate the bimetallic structure diagrammatically as a single layer. This is simply for the purpose of simplifying these reduced-scale drawings. It is to be understood, however, that the invention is also applicable to mono-metallic discs and discs of other numbers of layers but of the same shapes as those shown.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As many changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. A spring plate comprising a metallic sheet part having a non-developable surface adapted to change shape abruptly upon reaching a predetermined internal stress, said surface extending to at least a substantial portion of the edge of said plate, at least one ear formed integrally with said plate, and a reinforcing rib extending from a central portion of said plate toward the edge thereof in such position that said rib traverses at least a part of said ear.

2. A spring plate comprising a metallic sheet part having a non-developable surface adapted to change shape abruptly when at least a portion of said surface reaches a predetermined internal stress, and a developable surface in the 6 shape of a formed rib, said rib extending from a central portion of said non-developable surface outwardly toward an edge of said plate, and at least one ear formed integrally with said plate, said rib traversing at least a portion of said ear.

8. A control device comprising a base, a snapacting spring plate, said plate comprising a metallic sheet part having a non-developable surface adapted to change shape abruptly upon reaching a predetermined internal stress, said surface extending to at least a substantial portion of the edge of said plate, at least one ear formed integrally with said plate, and a reinforcing rib extending from a. central portion of said sheet toward the edge thereof in such position that said rib traverses at least part of said ear, said plate being mounted on said base, and control means actuated by another portion of said plate. 4. A control device comprising a base, mounting means on said base, a spring plate, and other means controlled by said spring plate, said spring plate having a metallic sheet part having a nondevelopable surface adapted to change shape abruptly when at least a portion of said surface reaches a predetermined internal stress, and having a developable surface in the shape of a formed rib, said developable surface being bounded, at least in part, by a re-entrant portion of the periphery of said non-developable surface and at least one ear formed integrally with said plate, said rib including at least a portion of said ear, said spring plate being mounted on said base by attaching said ear to said mounting means, and said other means being controlled by the motion of a portion of said plate remote from said ear.

5. A thermostatic control device comprising a base, mounting means on said base, a thermostatic plate, and other means controlled by said thermostatic plate, said thermostatic plate comprising a composite thermostatic sheet having a non-deyelopable-surface adapted to change shape abruptly upon reaching a predetermined temperature, and a developable surface in the shape of a formed rib, said rib extending from a central portion of said non-developable surface outwardly toward an edge of said plate, and at least one ear formed integrally with said plate, said rib including at least a portion of said ear, said thermostatic plate being mounted on said base by attaching said ear to said mounting means, and said other means being controlled by motion of a portion oi. said plate remote from said ear.

6. A switch comprising a base, a mounting means on said base, a spring plate, a contact actuated by said plate, and a cooperating contact mounted on said base, said spring plate comprising a metallic sheet part having a non-developable surface adapted to change shape abruptly when at least a portion of said plate reaches a predetermined internal stress, and a developable surface in the shape of a formed rib, said rib extending from a central portion of said non-developable surface outwardly toward an edge of said plate, and at least one ear formed integrally with said plate, said rib including at least a portion of said ear, said plate being mounted on said base by attaching said ear to said mounting means.

7. A switch comprising a base, a spring plate, a contact actuated by said plate, and a cooperating contact mounted on said base, said plate comprising a metallic sheet part having a non-developable surface adapted to change shape abruptly upon reaching a predetermined internal stress, said surface having a periphery of which a portion is re-entrant, at least one ear formed comprising a Y sheet of composite thermostatic integrally with said plate, and a reinforcing rib metal having a non-developable surface and at contiguous with the re-entrant periphery of said least one ear formed integrally with said plate, non-developable surface, in such position that and reinforcing means for stifiening said ear and said rib traverses at least part of said ear, said a portion of said plate, said means comprising a plate being mounted on said base by attaching rib formed integrally in said ear and plate by said ear to said base. crimping at least a portion of said ear and plate 8. A thermostatic switch comprising a base. a to form a trough-like channel extending across thermostatic plate, a contact actuated by said said ear and toward the center of said plate, said plate, and a cooperating contact mounted on said plate being mounted on said base by attaching base, said plate comprising a composite thermosaid ear to said stud, and means for adjusting the static sheet part having a non-developable suroperating temperature of said plate, said means face adapted to change shape abruptly upon comprising a cut-away portion of said stud which reaching a predetermined temperature, and a permits bending of said stud. developable surface in the shape of a formed rib, 11. A snap-acting element comprising a, persaid rib extending from a central portion of said manently set dished metallic disc having at least plate outwardly toward an edge of said plate, one outwardly projecting ear and a central hole, and at least one ear formed integrally with said and an integral stiffening rib formed of the maplate, said rib including at least a portion of said terial of the disc and extending substantially ear, said plate being mounted on said base by radially from the outer edge of the ear to the cenattaching said ear to said base. tral hole, the disc being inherently snap-acting 9. A thermostatic switch'comprising a base, a and capable of retaining a dished shape indestud mounted on said base, a thermostatic plate, pendently of the effect of the rib.

a contact carried by said plate and cooperating HAROLD M. WILSON. with a contact mounted on said base, said plate comprising a sheet of composite thermostatic REFERENCES CITED metal having av non-developable surface and at The following references are of record in the least one ear formed integrally with said plate, m of thi patent; and reinforming means for stiffening said ear and .a portion of said plate, said means compris- UNITED STATES PATENTS ing a rib formed integrally in said ear and plate Number Name Date by crimping at least a portion of said ear and 1,895,591 Spencer Jan. 31, 1933 plate to form a trough-like channel extending 1,895,592 Spencer Jan. 31, 1933 across said ear and toward a central portion of 1,983,345 Vaughn Jan. 15, 1935 said plate, said plate being mounted on said base 2,157,560 Neece May 9, 1939 by attaching said ear to said stud, and means for 2,258,375 Arras Oct. 14, 1941 adjusting the operating temperature of said plate. 2,264,902 Hill Dec. 2, 1941 10. A thermostatic switch comprising a base, 2,299,562 Burch Oct. 20, 1942 a stud mounted on said base, a thermostatic plate, 2,317,831 Vaughan et a1. Apr. 2'7, 1943 a contact carried by said plate and cooperating 2,340,615 Rath Feb. 1, 1944 with a contact mounted on said base, said plate 2,363,280 Arnold Nov. 21, 1944 

